Experimental Study on the Shear Mechanical Properties of Loess Modified by Rubber Particles Combined with Cementing Material

Rubber particles have been proven to have the advantages of improving the energy absorption effect and enhancing the friction between soil particles when used to modify the soil. The rubber-modified soil technology also provides a new solution for the pollution-free disposal of waste rubber. However, when rubber particles are used to modify collapsible loess, they cannot significantly enhance its strength. Previous studies have not systematically clarified whether combining rubber particles with different cementation mechanisms can overcome this limitation, nor compared their shear mechanical effectiveness under identical conditions. In view of this, a dual synergistic strategy is implemented by combining rubber with lime and rubber with enzyme-induced calcium carbonate precipitation (EICP). Direct shear tests and scanning electron microscopy are used to evaluate four modification approaches: rubber alone, lime alone, rubber with EICP, and rubber with lime. Accordingly, shear strength, cohesion, and internal friction angle are quantified. At a vertical normal stress of 100 kPa and above, samples modified with rubber and lime (7–9% lime and 6–8% rubber) achieve peak shear strength values of 200–203 kPa, representing an 86.4% increase compared to rubber alone. Microscopic analysis reveals that calcium silicate hydrate gel effectively anchored rubber particles, forming a composite structure with a rigid skeleton and elastic buffer. In comparison, the rubber and EICP group (10% rubber) shows a substantial increase in internal friction angle (24.25°) but only a modest improvement in cohesion (16.5%), which is due to limited continuity in the calcium carbonate bonding network. It should be noted that the performance of EICP-based modification is constrained by curing efficiency and reaction continuity, which may affect its scalability in conventional engineering applications. Overall, the combination of rubber and lime provided an optimal balance of strength, ductility, and construction efficiency. Meanwhile, the rubber and EICP method demonstrates notable advantages in environmental compatibility and long-term durability, making it suitable for ecologically sensitive applications. The results offer a framework for loess stabilization based on performance adaptation and resource recycling, supporting sustainable use of waste rubber in geotechnical engineering.